Test review 2
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The octet rule says that atoms can become stable (do not want to lose or receive
electrons) by having eight electrons in their outer energy level.
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An ion is an atom or group of combined atoms that has a charge because of the
loss or gain of electrons.
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Ionic compounds, like table salt: NaCl, usually form crystals of repeating ion
pairs by combining a metal with a nonmetal element. NACL crystals form
repeating patterns of positive and negative ions to maximize the distance
between like charges
The attraction of two atoms for a shared pair of electrons is called a covalent bond
Examples of covalent boding:
• If two chlorine atoms combine, they share a single pair of electrons, and each
atom attains a stable octet configuration.
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Two oxygen atoms share two pairs of electrons to form O2, and two nitrogen
atoms share three pairs of electrons to form N2.
Acids and bases
• acid is a substance that produces hydrogen ions when it dissolves in water.
Example:
HCL H+ + CL _
• A base is a substance that produces hydroxide ions, OH –, when it dissolves in
water. Example:
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Strong acid: acid fully dissociates in water to form hydrogen ions (H+)
Strong base: base fully dissociates in water to form hydroxide ions (OH-)
Weak base: some of the base dissociates and becomes partially ionized.
Indicator: tells whether something is basic or acidic. For example cabbage juice is
an indicator. It tunes red in acidic solution.
Exothermic/endothermic reaction
In an endothermic chemical reaction, energy in the form of heat is absorbed in the
process.
Example: Photosynthesis is an example of endothermic reaction. Light energy is
absorbed by the plant.
In an exothermic chemical reaction, energy in the form of heat is given off in the process.
Example: cellular respiration or hot packs made in the lab are examples of exothermic
reaction.
Based on the following chart we see that products have more energy than reactant in an
endothermic reaction
Based on the following chart we see that reactants have more energy than products in an
exothermic chemical reaction.